1. Field of the Invention
The present invention relates to a waveform generator that can generate a desired waveform and a testing device including the waveform generator.
2. Description of the Related Art
A testing device for testing electric devices each having an A-D converting unit that can convert an analog signal to a digital signal includes a waveform generator that generates a testing waveform to be used for testing the A-D converting unit of the electric device.
FIG. 1 is a block diagram showing a conventional waveform generator 10. The waveform generator 10 includes a waveform memory 20, a reference clock generator 22, a D-A converting unit 24 and a waveform outputting unit 26. The waveform memory 20 stores testing waveform data to be used for generating a testing waveform. The waveform memory 20 outputs the testing waveform data to the D-A converting unit 24 at a time of a reference clock supplied from the reference clock generator. The D-A converting unit 24 converts the testing waveform data into a voltage value at the time of the reference clock. The waveform outputting unit 26 outputs the testing waveform obtained by removing a predetermined frequency component from the voltage value supplied from the D-A converting unit 24 at the time of the reference clock.
FIG. 2(a) shows the voltage value output from the D-A converting unit 24 included in the waveform generator 10 shown in FIG. 1. The D-A converting unit 24 converts the testing waveform data supplied from the waveform memory 20 into the voltage value and outputs the obtained voltage value at the time of the reference clock. Thus, the D-A converting unit 24 outputs the voltage value that changes at a period of the reference clock.
FIG. 2(b) shows the testing waveform output from the waveform outputting unit 26 included in the waveform generator 10 described referring to FIG. 1. The waveform outputting unit 26 outputs the testing waveform after removing the predetermined frequency component from the waveform shown in FIG. 2(a).
In a case of generating a testing waveform having a high frequency, it was necessary for the conventional waveform generator 10 to include the D-A converting unit 24 that can operate at high speed. Also, in the conventional waveform generator 10, it was difficult to approximate the testing waveform with high accuracy because the conventional waveform generator 10 generates voltage values approximating the voltage values of the testing waveform at constant intervals.
Therefore, it is an object of the present invention to provide a waveform generator and a testing device which are capable of overcoming the above drawbacks accompanying the conventional art. The above and other objects can be achieved by combinations described in the independent claims. The dependent claims define further advantageous and exemplary combinations of the present invention.
According to the first aspect of the present invention, a waveform generator for generating a desired waveform comprises: a rectangular wave generating unit operable to generate a plurality of rectangular waves; and a waveform synthesizing unit operable to synthesize the rectangular waves to generate a multi-level synthesized wave, wherein the desired waveform is generated based on the synthesized wave.
The rectangular wave generating unit may generate the rectangular waves in such a manner that each of the rectangular waves rises at a desired rising timing based on the desired waveform and falls at a desired falling timing based on the desired waveform. In addition, the waveform generator may further comprise a filter operable to remove a predetermined frequency component from the synthesized wave.
The rectangular wave generating unit may include a waveform memory operable to store information regarding a voltage value of each of the rectangular waves. The rectangular wave generating unit may further include: a timing memory operable to store the rising and falling timings of each of the rectangular waves; and a rectangular wave outputting unit operable to output the rectangular waves based on the information and the rising and falling timings of each of the rectangular waves.
The rectangular wave generating unit may include: a plurality of waveform memories each operable to store information of a voltage value of a corresponding one of the rectangular waves; a plurality of timing memories each operable to store the rising and falling timing of a corresponding one of the rectangular waves; and a rectangular wave outputting unit operable to output the rectangular waves based on the information of each of the rectangular waves and the rising and falling timings of each rectangular wave.
The rectangular wave outputting unit may be a D-A converter that converts the information of the voltage value into an analog signal. The waveform generator may further comprise a timing adjuster operable to delay a reference clock based on the rising and falling timings of each of the rectangular waves stored in the timing memory (memories).
The waveform generator may further comprise a voltage controller operable to control the amplitude of each of the rectangular waves based on the desired waveform. The waveform synthesizing unit may perform an operation for the voltage value of each of the rectangular waves.
The rectangular wave generating unit may convert the information of the voltage value stored in the waveform memory into an N-digit base-M number (N and M are integers equal to or larger than 2), generate Nth number of logical voltage values that are voltage values specifying logical values corresponding to the N-digit base-M number, and supply the logical voltage values to the waveform synthesizing unit. Moreover, the rectangular wave generating unit may include Nth number of rectangular wave generators operable to generate the M-valued logical voltage values, respectively, and the waveform synthesizing unit obtains (1/M)K times the logical voltage value supplied from the K-th waveform generator (K is an integer equal to or larger than 1 but does not exceed N) and synthesizes (1/M)K times the logical voltage values so as to generate the desired waveform.
The waveform synthesizing unit may include a ladder having the Nth number of logical voltage values as inputs. In this case, the Nth number of rectangular wave generators are electrically connected to Nth number of nodes, respectively, the nodes are connected to each other via resistors each having a predetermined resistance, the K-th logical voltage value to (1/M) times at the K-th node, and a voltage value at the K-th node drops to (1/M) times at the (Kxe2x88x921)th node.
The waveform synthesizing unit may include a ladder having the Nth number of logical voltage value as inputs. In this case, the J-th rectangular wave generator (J is an integer equal to or larger than 1 but does not exceed (Nxe2x88x921)) is connected to (Nxe2x88x921) nodes; the nodes are connected to each other via resistors each having a predetermined resistance; the N-th rectangular wave generator is connected to the (Nxe2x88x921)th node; the N-th logical voltage value falls to (1/M) times the N-th logical voltage value at the (Nxe2x88x921) th node; the J-th logical voltage value drops to (1/M) times at the J-th node; and a voltage value at the J-th node drops to (1/M) times at the (Jxe2x88x921)th node.
According to the second aspect of the present invention, a testing device for testing an electric device having an A-D converting unit that converts an analog signal to a digital signal, comprises: a rectangular wave generating unit operable to generate a plurality of rectangular waves; a waveform synthesizing unit operable to synthesize the rectangular waves to generate a multi-level synthesized wave; and a waveform generator operable to generate a testing waveform used for testing the electric device based on the synthesized wave, wherein the testing waveform is applied to the electrical device so as to test the electric device based on an output value of the electric device to which the testing waveform is applied.
The rectangular wave generating unit may generate the rectangular waves in such a manner that each rectangular wave rises at a desired rising timing based on a desired waveform and falls at a desired falling timing based on the desired waveform. The testing device may further comprise a filter operable to remove a predetermined frequency component from the synthesized wave.
The rectangular wave generating unit may convert information of a voltage value of each of the rectangular waves stored in a waveform memory into an N-digit base-M number (N and M are integers equal to or larger than 2) , generate Nth number of logical voltage values that are voltage values specifying logical values corresponding to the N-digit base-M number, and supply the logical voltage values to the waveform synthesizing unit.
The rectangular wave generating unit may include Nth number of rectangular wave generators operable to generate the M-valued logical voltage values, respectively, and the waveform synthesizing unit obtains (1/M)K times the logical voltage value supplied from the K-th waveform generator (K is an integer equal to or larger than 1 but does not exceed N) and synthesizes (1/M)K times the logical voltage values so as to generate the desired waveform.
The waveform synthesizing unit may include a ladder having the Nth number of logical voltage values as inputs. In this case, the Nth number of rectangular wave generators are electrically connected to Nth number of nodes, respectively; the nodes are connected to each other via resistors each having a predetermined resistance; the K-th logical voltage value drops to (1/M) times at the K-th node; and a voltage value at the K-th node drops to (1/M) times at the (Kxe2x88x921)th node.
The waveform synthesizing unit may include a ladder having the Nth number of logical voltage value as inputs. In this case, the J-th rectangular wave generator (J is an integer equal to or larger than 1 but does not exceed (Nxe2x88x921)) is connected to (Nxe2x88x921) nodes; the nodes are connected to each other via resistors each having a predetermined resistance; the N-th rectangular wave generator is connected to the (Nxe2x88x921)th node; the N-th logical voltage value at the (Nxe2x88x921) th node is (1/M) times the N-th logical voltage value; the J-th logical voltage value drops to (1/M) times at the J-th node; and a voltage value at the J-th node drops to (1/M) times at the (Jxe2x88x921)th node.
The testing device may further comprise: a DC tester operable to conduct a DC test of the electric device; a selection unit operable to electrically connect one of the DC tester and the rectangular wave generating unit to the waveform synthesizing unit; and a switching unit operable to switch whether or not the rectangular wave generating unit is electrically connected to the waveform synthesizing unit. In addition, the selection unit may electrically connect either the DC tester or one of the rectangular wave generators having the smallest impedance from the electric device to the rectangular wave generator to the waveform synthesizing unit, and the switching unit may switch whether or not others of the rectangular wave generators are electrically connected to the waveform synthesizing unit.
According to the third aspect of the present invention, a semiconductor device including a testing unit for testing a device unit having an A-D converting unit that converts an analog signal to a digital signal, comprises: a rectangular wave generating unit operable to generate a plurality of rectangular waves; a waveform synthesizing unit operable to synthesize the rectangular waves to generate a synthesized wave; a waveform generator operable to generate a testing waveform used for testing the A-D converting unit based on the synthesized wave; the device unit to which the testing waveform is applied; and the testing unit operable to test the A-D converting unit based on an output value of the device unit to which the testing waveform is applied.
The waveform generating unit may generate the rectangular waves in such a manner that each rectangular wave rises at a desired rising timing based on a desired waveform and falls at a desired falling timing based on the desired waveform. In addition, the semiconductor device may further comprise a filter operable to remove a predetermined frequency component from the synthesized wave.
According to the fourth aspect of the present invention, a waveform generation method for generating a desired waveform, comprises the steps of: generating a plurality of rectangular waves; synthesizing the rectangular waves to generate a multi-level synthesized wave; and generating the desired waveform based on the synthesized wave.
The step of generating the rectangular waves may include the step of generating the rectangular waves in such a manner that each rectangular wave rises at a desired rising timing based on the desired waveform and falls at a desired falling timing based on the desired waveform.
The step of generating the multi-level synthesized wave may include the step of calculating voltage values of the rectangular waves to generate the multi-level synthesized wave. In addition, the waveform generation method may further comprise the step of removing a predetermined frequency component of the synthesized wave after the step of generating the multi-level synthesized wave.
The summary of the invention does not necessarily describe all necessary features of the present invention. The present invention may also be a sub-combination of the features described above. The above and other features and advantages of the present invention will become more apparent from the following description of the embodiments taken in conjunction with the accompanying drawings.